The energy density of batteries is proportional to the operating voltage. In supercapacitors (i.e., electrochemical double-layer capacitors) the energy density is proportional to voltage squared. With a greater demand for increased energy densities in electrochemical energy storage devices, significant improvements can be made by increasing the voltage ratings of such devices. An important contributing factor to the voltage limitation of electrochemical energy storage devices is the stability of the electrolyte solvent. At increased voltages, the electrolyte solvent may break down and increase in resistance. As a result, loss of charge storage capability (capacity), gassing and device end of life may be reached. Therefore, improving the voltage rating of such devices is highly dependent on the electrolyte system used. Increasing the oxidation resistance of solvents may widen the potential window of the electrolyte, defined as the potential difference between which significant oxidation and reduction current occurs, and can be very useful in electrochemical applications such as batteries, supercapacitors, chemical sensing and common reduction-oxidation electrochemistry.